Technical Field
An aspect of the present invention relates to an image reading apparatus.
Related Art
A sheet conveying device is provided, for example, to an image reading apparatus. Typically, in the image reading apparatus, a sheet is picked up from an original sheet placing tray and conveyed along a sheet convey path in a predetermined conveying direction. The sheet convey path is passing an image reading section. When the sheet passes through the image reading section, an image formed on the sheet is read by an image reading unit.
Generally, the sheet conveying device has a roller unit for conveying the sheet on an upstream side, in the sheet conveying direction, with respect to the image reading section. Such a roller unit typically has three rollers, which are arranged to be rotatable about a rotation axis extending in a sheet-width direction, which is perpendicular to the sheet convey direction. The three rollers are arranged in the sheet-width direction in a spaced manner. When a sheet of which the width extends over the three rollers (hereinafter, such a sheet will be referred to as a normal size sheet) is conveyed, the normal sheet contacts circumferential surfaces of the three rollers. Thus, the normal size sheet receives a conveying force from the three rollers.
If a sheet of which width is smaller than a distance between two rollers respectively arranged at both sides, among the three rollers (hereinafter, such a sheet will also be referred to as a small size sheet) is conveyed such that the center of the sheet in its width direction is aligned to the center of the conveyance path, the small size sheet only contacts a circumferential surface of one roller arranged at a central portion. Therefore, a conveying force applied by the central roller to the small size sheet is less than the conveying force the normal size sheet receives from three rollers. As a result, when the small size sheet is conveyed, in comparison with a case where the normal size sheet is conveyed, a speed of the sheet when passing through the image reading section might be lowered. In such a case, an image of the small size sheet read by the image reader unit may be expanded in the sheet conveying direction.
According to aspects of the invention, there is provided an image reading apparatus, which has a separation section configured to supply a sheet one by one, at least three driving rollers arranged on a downstream, in a sheet conveying direction, of the separation section and configured to convey the sheet, at least three driven rollers configured to be urged by the driving rollers and driven to rotate by rotation of the driving rollers, respectively, and an image reader unit configured to read an image of the sheet conveyed in the conveying direction. The at least three driven rollers are arranged at a central portion and both side portions in a sheet width direction, and sheet conveying forces by one of the at least three driven rollers and one of the at least three driving rollers arranged at the central portions in the sheet width direction is greater than sheet conveying forces by others of the at least three driven rollers and others of the at least three driving rollers arranged at both side portions in the sheet width direction.
According to aspects of the invention, it is possible to suppress a situation that the conveying force applied to the small size sheet becomes insufficient. As a result, even the small size sheet can be conveyed at an appropriate conveying speed.